(1) Field of the Invention
This invention relates to a laser recording apparatus in which optical adjustment can be made easily.
(2) Description of the Prior Art
Generally, in a laser recording apparatus of this type, when recording is to be effected, for example, on a hard copy, as shown in FIG. 1 of the accompanying drawings, a laser beam emitted from a laser light source 1 is deflected by a mirror 2, passes through an optical system 3 for reducing the width of a parallel light beam, is intensity-modulated by an acousto-optical element 4 on the basis of information to be recorded, passes through an optical system 5 for enlarging the width of the parallel light beam and via a mirror 6 to a rotational polygon mirror 7. Then, the laser beam is subjected to main scanning on the rotational polygon mirror 7 and is imaged on a recording surface 9 through an f.theta. lens system 8. The mirrors 2 and 6 are for deflecting the laser beam to effectively utilize the space, and all elements including these mirrors are disposed on a base plate 10.
The acousto-optical element 4 is generally disposed as shown in FIGS. 2A and 2B, and when the laser beam Lo (which is parallel to the optical axis of the optical system 3) is caused to enter the acousto-optical element at an angle of incidence .theta., the intensity-modulated lst-order diffracted light L.sub.1 (which is parallel to the optical axis of the optical system 5) emerges from the acousto-optical element at an angle of emergence 2.theta.. Accordingly, in an apparatus utilizing the intensity-modulated 1st-order diffracted light L.sub.1, it is necessary that the angle formed between the optical axes forward and rearward of the acousto optical element 4 (the optic axis of the optical system 3 and the optical axis of the optical system 5) be 2.theta.. .theta. is a slight angle less than 1.degree., but must be delicately adjusted so that the ratio of the maximum intensity of the lst-order diffracted light L.sub.1 to the maximum intensity of the 0-order diffracted light Lo' is, e.g. 80% or more. The maximum intensity of the 0-order light Lo' is the intensity of the light Lo' when no voltage is applied to the acousto-optical element 4.
Presently, the adjustment of this angle must be effected on the base plate 10 with respect to each element of the optical system subsequent to the acousto-optical element 4, however, this adjustment is very difficult and time-consuming.
There is also a disadvantage in this arrangement in that when the adjustment of the acousto-optic element 4 is again to be effect ed as during the interchange of the laser after the adjustment has been completed, the difficult adjustment must also again be made with respect to each optical element subsequent to the acousto-optical element 4.